In an electric vehicle using an electric motor as a running drive source, the motor operates as a generator during deceleration regeneration, so that a resulting regenerative electric power can be used for charging a battery, and the motor acts as resistance against rotation of drive wheels, that is, the motor can be utilized as a regenerative brake.
As disclosed, for example, in the following Patent Document 1, a three-phase motor is generally used as an electric vehicle driving motor. This three-phase motor is configured to be driven by an electric power which is supplied from a battery and subjected to DC-AC conversion through an inverter. On the other hand, during deceleration regeneration, the inverter functions as a converter to convert a regenerative electric power generated by the motor into a DC power, and supply the DC power to the battery.
The three-phase motor usable as a running drive source of an electric vehicle comprises a first winding and a second winding provided on a per-phase basis and connected in series. In some cases, this type of three-phase motor is used while being switched between two types of current conduction modes: a high speed mode in which a current is conducted through only the first winding for each phase; and a low speed mode in which a current is conducted through both of the first and second windings for each phase.
Specifically, when a current is conducted through only the first winding, a total number of turns in a current conduction line for each phase is reduced, and thereby an induced voltage to be produced in the motor becomes relatively low. This allows a current to more easily flow from the battery to the motor, so that the motor can be rotated at a high speed. On the other hand, when a current is conducted through both of the first and second windings, the total number of turns in the current conduction line for each phase is increased, and thereby the induced voltage to be produced in the motor becomes relatively high. Thus, the current flow from the battery to the motor is suppressed, so that the motor is rotated at a relatively low speed.
Meanwhile, in an electric vehicle equipped with this type of three-phase motor as a running drive source, during deceleration under a condition that a shift range is set in a running range, a braking force by regenerative braking and a regenerative electric power to be supplied from the motor to the battery are controlled by controlling the inverter.
On the other hand, for example, when a driver does not want to activate the regenerative braking, the vehicle can be decelerated under a condition that the shift range is set in a neutral range. In this case, generally, the inverter control is not executed because there is no need to perform the deceleration regeneration.